Mentioned only by Irwin, who says:
“Major Clarinet is a louder form
[of Clarinet]”, and
“Major Clarinet and
Minor Clarinet
have somewhat different meanings
[from Solo Clarinet],
not always implying the solo tonality.”

Examples

Major Clarinet 8', Gallery Organ IV; Convention Hall, Atlantic City, New Jersey; USA;
Midmer-Losh 1929-32. This is the only known example.